1. Field of the Invention
This invention relates to a method of removing organic chloride contaminants from hydrocarbon feedstocks. In particular, the invention is concerned with a method of protecting metal-containing zeolite catalysts against the deleterious effects of organic chlorides by use of a novel guard bed catalyst.
Hydrocarbons of natural or synthetic origin as generally available are often contaminated by the presence therein of impurities in substantial amounts, the removal of which is essential before such hydrocarbons can be efficiently employed as starting materials in processes of converting such hydrocarbons to move valuable derivatives thereof. In particular, chloride impurities in organically combined form may be of natural origin or have been introduced into the hydrocarbon charge during a chemical treating or processing operation.
The deleterious effects of halogens on catalytic function, in particular, on metal-containing hydrocarbon reforming catalysts is known and attempts have been made to treat the hydrocarbon charge for removal of the halogen components prior to reforming the charge. It has been found, for example, that organic chlorides can have a detrimental effect on the activity of the metal-containing reforming catalysts to such an extent that the catalyst loses its ability to promote the various individual reforming reactions. In addition, the catalyst may lost its ability to promote the desired reforming reactions such that the catalyst loses the desired selectivity for desired products.
Chloride contamination is particularly harmful in processes involving the disproportionation and alkylation of toluene to para-xylene and para-ethyltoluene over ZSM-5 zeolite catalysts which also contain magnesium. Such processes are disclosed in U.S. Pat. Nos. 3,972,832; 4,034,053; 4,128,592; 4,137,195; 4,278,827 and 4,447,666, the entire contents of which are herein incorporated by reference. Chloride contamination of the toluene feedstock can alter the selectivity of the process so as to reduce the production of the more important para isomer.
2. Description of the Prior Art
As stated above, there have been previous attempts to remove organically combined halogens from hydrocarbon charge stocks. For example, U.S. Pat. No. 2,413,871 discloses the removal of organically combined chlorine from hydrocarbons by subjecting the hydrocarbon to the action of a mixture of alumina in a suitably active form such as bauxite and quick lime under conditions such as to effect decomposition of the organic chloride compounds. U.S. Pat. No. 2,481,300 discloses that contaminating amounts of impurities such as organically combined halogen can be removed substantially completely from hydrocarbons by contacting the hydrocarbons with a catalyst comprising active carbon in combination with an alkaline compound of an alkali and/or alkaline earth metal. Alkaline earth metals which are specifically mentioned include calcium, barium, and strontium.
U.S. Pat. No. 2,951,804 discloses a method for the removal of acidic organic contaminants from reforming chargestocks by contacting the chargestock with an activated alumina having impregnated thereon an added base such as the hydroxides of alkali metals and alkaline earth metals, the preferred bases being the hydroxide of either sodium or potassium.
U.S. Pat. No. 2,967,819 also discloses a method for protecting hydrocarbon reforming catalysts against the deleterious effect of halogen compounds by contacting the hydrocarbon charge with certain alkaline earth metal compounds prior to contacting the charge material with the metal-containing reforming catalyst. The charge is contacted with alkaline earth metal compounds such as calcium oxide, calcium sulfide, barium oxide, or barium sulfide or mixtures of two or more of these compounds. The compounds or mixture thereof are in the form of solid pellets or granules. In order to provide mechanical strength to the alkaline earth metal compound pellets, such compounds may be mixed prior to pelleting with an inert material such as alumina or magnesia.
U.S. Pat. No. 3,278,266 discloses the separation of hydrogen halides from hydrocarbons by contacting the hydrocarbon charge with a diacid base deposited on a highly porous acid resistant support. Suitable diacid bases include magnesium, calcium, strontium, and barium in the form of their respective oxides or hydroxides. Generally, the alkaline earth base or the diacid base deposit will be between 5 to 20% by weight although amounts as high as 35% and as low as 1% may be used.
U.S. Pat. No. 3,898,153 discloses as a chloride scavenger the use of a caustic solution or a copper guard catalyst.
U.S. Pat. No. 3,935,295 discloses a process for removing hydrogen chloride from a hydrocarbon stream by passing the hydrocarbon stream through a bed of dried and discrete absorbent particles consisting essentially of zinc oxide, a basic compound of calcium and an inert binder.
U.S. Pat. No. 4,127,470 discloses a process of removing sulfur compounds from hydrocarbon feedstocks by contacting the feed with an alkali metal or alkaline earth metal including calcium, barium and magnesium oxides. Suitable supports can be employed such as alumina whereby the supported systems can be prepared by individually impregnating the support which is to be utilized with each reagent. Preferably, the alkaline earth metal compound is utilized as a support for the alkali metal compounds.
U.S. Pat. No. 4,341,745 discloses the removal of acid gases from waste gases by contacting the gases with an absorbent which is a direct reaction product from a mixture of red mud and an alkaline earth metal hydroxide or aluminum oxide. Calcium is the only alkaline earth metal compound specifically disclosed in the patent.
Other methods of dehydrochlorinating (HCl elmination) are known. Note "Catalytic Reduction of Organic Chlorine Compounds in Hydrogen Stream by 50 percent Ni on Kieselguhr Catalysts", [Mokrousova et al, Kinet-Katal, 16 #3, 796-797 (1975)]; "Dehydrochlorination of Chloroalkanes on Solid Acids and Bases" [Mochida et al. J. Cat. 43 (1976); J. Org. Chem., 32 (1967), J. Org. Chem. 33 (1968)]; and SRI Report #102 "Disposal and Recovery of Waste Organo Chlorides" (1976).